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ri                            BARRIERS TO DISTRIBUTION                          79
Jaguar to America, and so forth. The entire expanse of country
which is inhabited by an animal is called its area of distribution.
Such areas are larger or smaller. The Lion ranges over the whole
of Africa, a small part of India, and some neighbouring countries ;
on the other hand, the Insectivore Solenodon is limited to Cuba
and Hayti, a separate species to each. Among other groups of
animals are instances of an even more restricted range. There
are humming-birds confined to the slopes of a single mountain.,
and fishes limited in their range to a single small lake.
A species may be found everywhere within the area of its
distribution, or it may be confined to a number of limited tracts
within that area. In this case it is usual to speak of " stations."
In such cases the species in question is generally suited to some
particular kind of environment. Thus the Otter and other
aquatic mammals will only be found where there is water; and
intervening tracts of waterless country will contain no Otters.
Goats and Chamois live only upon mountains ; the intervening
plains are destitute of them. This discontinuity of distribution
within the area is very general. But a discontinuity of area is
also seen—not so commonly however; and, indeed, when it does
occur, it is a matter of a genus and not of a species. Thus the
Tapir is found in the East Indies on the one hand and in South
and Central America on the other, being absent in the inter-
mediate tracts.
It is clear that tracts of country eminently suitable for the
housing of a particular mammal do not always possess that kind,
or even an allied form. Africa, for example, possesses no arboreal
Anteaters; there are no Anteaters at all (of the order Edentata)
in Australia, though there are plenty of ants for them to feed upon,
and tropical conditions of climate prevail. !But as in these cases
the inference may be denied on the grounds that no experiments
exist to prove or to disprove the assertion, the matter may be
better emphasised by such cases as the introduction of the Habbit
into Australia, and various mammals, such as Groats, into oceanic
islands. The plague caused by the former is a matter of notoriety.
But although climate and conditions and animal inhabitants do
not march accurately together, there is certainly some connexion
between temperature and the range of animals. Mr. Lydekker
writes on this point as follows : * The llama-like afllrnals, re-
spectively known as vicunas and gtmnacos, are met wifcii In